1. Field of the Invention
The present invention relates to apparatus for making or breaking electrical contact in an electrical circuit, and more particularly to a switch contact structure of exceedingly simple construction, suitable for infinite variations of pressure, pre-travel and post-travel distance, and power requirements.
2. Description of the Prior Art
In general, switches wherein one or more electrical contacts are formed of expanded compression (coil) springs are known. For example, U.S. Pat. No. 4,209,682, issued to the present inventor on June 24, 1980, describes a momentary contact switch wherein one contact comprises an expanded compression spring having a transverse contact portion which effects a wiping contact with a conductive striking member when a push button is pressed. The transverse contact portion is flexible, and exerts continuous force against the striking member to provide a low bounce characteristic.
Another switch, which utilizes two concentric expanded compression springs as contacts is described in U.S. Pat. No. 3,773,996, issued to K. A. Sharf on Nov. 20, 1973. One of the springs includes a radial cross bar portion, located at the end or at some intermediate point on the spring, which engages the other spring when the springs are depressed.
U.S. Pat. No. 3,396,257 issued Aug. 6, 1968 to C. Vazquez describes the use of a vertically disposed tightly wound prestressed (compressed) coil spring and a stretched (expanded) coil spring as contacts. The tightly wound coil spring is disposed vertically, with one end fixed on the base of the switch. The expanded coil spring is disposed horizontally, offset from the tightly wound spring. The free end of the tightly wound coil spring is laterally displaced to bring it into electrical contact with the expanded coil spring. The pitch of the expanded coil spring is chosen so that the tightly wound spring makes a wiping contact with two of the coils of the expanded spring.
Other known switches utilize a compression spring as one contact, and a resilient, serpentine shaped metal strip disposed within the spring, as another contact. The serpentine member cooperates with a cammed surface on the interior of a push button, and is deformed (bowed) to effect contact with the spring when the push button is pressed. Such a switch is described in U.S. Pat. No. 3,809,839 issued on May 7, 1974 to S. Beddoe.
Another switch utilizing a compression spring for a contact is described in U.S. Pat. No. 3,699,296, issued to R. H. Harris on Oct. 17, 1972. In such switch a second contact is vertically disposed along one wall of the switch casing. Depression of a push button causes catastrophic buckling, or bowing of the compression spring to effect contact with the vertical member.
Other switches utilize a moving contact cooperating with horizontally disposed spring contacts. Examples of such switches are described in U.S. Pat. No. 3,207,870, issued Sept. 21, 1965 to J. R. Herrera et al and U.S. Pat. No. 3,745,269, issued to T. Arvai on July 10, 1973.
Other springs utilize a push button to cause an expansion of a compressed compression spring to effect wiping action with vertically disposed contacts. An example of such a switch is described in U.S. Pat. No. 1,333,115, issued Mar. 9, 1920 to L. H. Jones.
Other examples of switches utilizing compression spring contacts are described in U.S.. Pat. Nos. 2,436,123, issued Feb. 17, 1948 to E. Sines; 3,731,022, issued May 1, 1973 to T. J. Loftus; and 3,725,625 issued Apr. 3, 1973 to A. R. Pratt.
The prior art coil spring switches, however, tend to be relatively complex in structure, and relatively expensive to manufacture.